Mitochondrial dysfunction of cardiomyocytes causing impairment of cellularenergy metabolism induces apoptosis, and concomitant increase in cardiac endothelin-1 expression

It has been reported that at the end stage, apoptosis is involved in the pr ogression of heart failure. It is suggested that cardiac energy metabolism is impaired during the progression of heart failure. Although the mechanism of induction of apoptosis in the failing heart varies according to the mod el of heart failure, it is not known whether an impairment of energy metabo lism in cardiomyocytes is a primary cause of apoptosis. In this study, we a pplied mitochondrial inhibitors, such as rotenone, cobalt chloride and anti mycin A, which inhibit mitochondrial function at different sites of the mit ochondrial respiratory chain, to cardiomyocytes. All these reagents markedl y decreased 3-(4,5)dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide a ssay (MTT) reduction activity, an indicator of mitochondrial function, of c ardiomyocytes and greatly increased glucose consumption, suggesting that ca rdiac energy metabolism is switched from beta -oxidation of fatty acid to g lycolysis. It was shown that after 48-72 h of treatment with each reagent, apoptosis was shown to occur by DNA laddering and increase in caspase activ ity. Interestingly, each reagent with a different action site greatly activ ated caspase-3, but not caspase-8 activity, suggesting that mitochondria ar e involved in induction of apoptosis. On the other hand, within 24 h of the treatment, when apoptosis of cardiomyocytes was not observed, the treated cardiomyocytes showed a marked increase in preproendothelin-1 and atrial na triuretic peptide (ANP) gene expressions. In conclusion, the present study suggests that mitochondrial dysfunction with impaired energy metabolism ele vates gene expression of cardiac ET-1, an aggravating factor in heart failu re, and then finally induces apoptosis in cardiomyocytes. The finding of ma rked increases in expression of molecular markers (ET-1 mRNA and ANP mRNA) in the failing heart, followed by apoptosis in the treated cardiomyocytes s uggests that the inhibition of mitochondrial function of cultured cardiomyo cytes provides a possible new in vitro model of heart failure.